Selena Gomez Glows in White Bikini on Instagram (PHOTOS)

The singer posted a photo alongside two friends, all wearing white bikinis on the beach. Gomez, 26, can be seen smiling in one photo and hugging a friend in another.

"My best friend is getting married, so we celebrated her! Future Mrs. Lopez," she captioned the post.

The friend in question is Courtney Barry, according to a report from E! Online. Gomez, Barry and other friends traveled to Mexico over the weekend to celebrate the occasion. Barry posted her own photos from the trip, which showed Gomez horseback riding. She also shared a group shot, calling the trip "the best weekend" in the caption.

"had the best weekend celebrating with some of my closest lady friends. hard to explain the love and joy I've felt this season," she wrote.

According to a source, the group of friend spent a few day relaxing poolside. Gomez, who has been struggling with mental health issues, was said to be in a good place the entire time.

"They had an amazing few days with lots of girlfriend time by the pool," the insider shared. "Selena was in great spirits and looked healthy and happy. She was right in the middle of her friends eating chips and guacamole and drinking from a big bottle of water. They all positioned their chairs in a big circle and spent the day on the rooftop laughing and gossiping."

The source continued, "At night they had dinner on the beach and were treated to a fireworks show in the sky. They took lots of pictures together with a disposable camera and commemorated the weekend."

Gomez's trip with her pals was "an enjoyable few days" for her "and she seemed to really love being in the sun and just having girl time with her closest friends."

She and Barry have been friends for some time. The pair even have matching #1 tattoos, which they got to celebrate their friendship. Gomez shared a photo of the tattoo over the summer.

"And lastly, my actual #1 @courtneyjbarry you are an incredible woman," she wrote. "The way you handle life's most confusing moments is indescribable and graceful. You are moved by the littlest stories to the most heartbreaking ones, you will give someone your perfume if they say you smell nice, you are freaking hilarious and always stand firm in your faith, a loving sister, an amazing friend and a beautiful daughter. You are the definition of FEARFULLY and WONDERFULLY made baby!"